Molybdenum disilicide is a useful material well known to the prior art; it is one of the very few commercially feasible materials used in high-temperature heating elements for oxidizing environments. Thus, for example, U.S. Pat. No. 3,027,331 of Schrewelius discloses the preparation of electrical resistance heating elements from molybdenum disilicide.
The conventional method for making molybdenum disilicide is very expensive, requiring both costly reagents and a substantial amount of heat. In this prior art method, molybdenum and silicon are heated at a temperature of from between about 1,400 to about 1,600 degrees centigrade for at least about 6 hours.
The materials used in the conventional method are very expensive. Thus, referring to the 1990-1991 Alfa Catalog (available from Alfa Products, Ward Hill, Mass.), molybdenum powder in the 3-7 micron particle size range (reagent number 10030) costs ninety-eight dollars per kilogram, and silicon powder with particle size smaller than 325 mesh (reagent 12681) is one-hundred-thirty-four dollars per kilogram. The molybdenum silicide available from Alfa Products (reagent number 11549) costs four-hundred-twelve dollars per kilogram.
Several attempts have been made to reduce the cost of producing molybdenum disilicide. Thus, U.S. Pat. No. 2,982,619 of Long describes a process in which elemental molybdenum and elemental silicon are heated to a temperature of 1,100 degrees centigrade, at which point an exothermic reaction occurs. U.S. Pat. No. 3,056,658 of Brennan et al. describes an exothermic process in which elemental molybdenum is reacted with elemental silicon. The aforementioned Schrewelius patent also discloses a similar exothermic reaction.
Even though the Long, Brennan, and Schrewelius patents describe processes which are more energy-efficient than prior molybdenum disilicide processes, they still require the use of expensive raw materials, elemental molybdenum and elemental silicon.
One of the means available to control a self-sustaining, highly exothermic synthesis (SHS) process is to moderate it with a material which will control the reaction front features and its motion, affect the yield, and minimize production of undesired by-product. The diluent/moderator must slow the reaction front only to a specified extent; too much moderation may extinguish the front.
It is an object of this invention to provide a process for the preparation of molybdenum disilicide in which an exothermic reaction between the reagents used occurs in matter of seconds.
It is another object of this invention to provide a process for the preparation of molybdenum disilicide which utilizes inexpensive, readily available raw materials.
It is a further object of this invention to provide an highly exothermic reaction for the production of molybdenum disilicide in which the reaction rate is moderated by the use a diluent which is readily removable from the reaction product by leaching with water.